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642fa98976
This includes two new hidden commands: a 9p server, `podman machine server9p`, and a 9p client, `podman machine client9p` with `server9p` currently only configured to run on Windows and serve 9p via HyperV vsock, and `client9p` only configured to run on Linux. The server is run by `podman machine start` and has the same lifespan as gvproxy (waits for the gvproxy PID to die before shutting down). The client is run inside the VM, also by `podman machine start`, and mounts uses kernel 9p mount code to complete the mount. It's unfortunately not possible to use mount directly without the wrapper; we need to set up the vsock and pass it to mount as an FD. In theory this can be generalized so that the server can run anywhere and over almost any transport, but I haven't done this here as I don't think we have a usecase other than HyperV right now. [NO NEW TESTS NEEDED] This requires changes to Podman in the VM, so we need to wait until a build with this lands in FCOS to test. Signed-off-by: Matthew Heon <matthew.heon@pm.me>
81 lines
3.1 KiB
Go
81 lines
3.1 KiB
Go
// Copyright 2016 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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/*
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Package bpf implements marshaling and unmarshaling of programs for the
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Berkeley Packet Filter virtual machine, and provides a Go implementation
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of the virtual machine.
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BPF's main use is to specify a packet filter for network taps, so that
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the kernel doesn't have to expensively copy every packet it sees to
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userspace. However, it's been repurposed to other areas where running
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user code in-kernel is needed. For example, Linux's seccomp uses BPF
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to apply security policies to system calls. For simplicity, this
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documentation refers only to packets, but other uses of BPF have their
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own data payloads.
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BPF programs run in a restricted virtual machine. It has almost no
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access to kernel functions, and while conditional branches are
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allowed, they can only jump forwards, to guarantee that there are no
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infinite loops.
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# The virtual machine
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The BPF VM is an accumulator machine. Its main register, called
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register A, is an implicit source and destination in all arithmetic
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and logic operations. The machine also has 16 scratch registers for
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temporary storage, and an indirection register (register X) for
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indirect memory access. All registers are 32 bits wide.
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Each run of a BPF program is given one packet, which is placed in the
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VM's read-only "main memory". LoadAbsolute and LoadIndirect
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instructions can fetch up to 32 bits at a time into register A for
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examination.
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The goal of a BPF program is to produce and return a verdict (uint32),
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which tells the kernel what to do with the packet. In the context of
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packet filtering, the returned value is the number of bytes of the
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packet to forward to userspace, or 0 to ignore the packet. Other
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contexts like seccomp define their own return values.
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In order to simplify programs, attempts to read past the end of the
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packet terminate the program execution with a verdict of 0 (ignore
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packet). This means that the vast majority of BPF programs don't need
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to do any explicit bounds checking.
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In addition to the bytes of the packet, some BPF programs have access
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to extensions, which are essentially calls to kernel utility
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functions. Currently, the only extensions supported by this package
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are the Linux packet filter extensions.
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# Examples
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This packet filter selects all ARP packets.
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bpf.Assemble([]bpf.Instruction{
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// Load "EtherType" field from the ethernet header.
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bpf.LoadAbsolute{Off: 12, Size: 2},
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// Skip over the next instruction if EtherType is not ARP.
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bpf.JumpIf{Cond: bpf.JumpNotEqual, Val: 0x0806, SkipTrue: 1},
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// Verdict is "send up to 4k of the packet to userspace."
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bpf.RetConstant{Val: 4096},
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// Verdict is "ignore packet."
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bpf.RetConstant{Val: 0},
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})
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This packet filter captures a random 1% sample of traffic.
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bpf.Assemble([]bpf.Instruction{
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// Get a 32-bit random number from the Linux kernel.
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bpf.LoadExtension{Num: bpf.ExtRand},
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// 1% dice roll?
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bpf.JumpIf{Cond: bpf.JumpLessThan, Val: 2^32/100, SkipFalse: 1},
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// Capture.
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bpf.RetConstant{Val: 4096},
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// Ignore.
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bpf.RetConstant{Val: 0},
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})
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*/
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package bpf // import "golang.org/x/net/bpf"
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